The separation of halogen-organic pollutants from water, especially waste water, is becoming more important for toxicological and ecotoxilogical reasons. Thus, it is necessary to treat e.g. seepage water from waste dumps as well as ground water contaminated with halogen-organic pollutants. On the one hand, seepage water from waste dumps can have a very adverse impact on fauna and flora if it is passed without pretreatment into a waterway and, if it is introduced into a biological water-purification plant, it can severely disturb or even prevent its operation. On the other hand, seepage into the ground can result in contamination of the ground water, which can prevent the ground water from being used as a source of drinking water. The treatment of ground water contaminated with halogen-organic pollutants is necessary in order to prevent it from spreading.
The following physicochemical methods are currently available for the treatment of seepage water and ground water containing halogen-organic pollutants, which water also generally contains other organic and inorganic pollutants in a greater or lesser amount--cf. K. Leonhard in "Berichte aus Watergutewirtschaft und Gesundheitsingenieurwesen der Technischen Universitat Munchen" [Reports on Water-Quality Economy and Sanitary Engineering of the Technical University of Munich] No. 74 (1987), pp. 230-237: Liquid-Liquid Extraction, Stripping with Steam and Air, Mono- or Bidistillation, Adsorption onto Activated Carbon.
Because of the complex composition of the water in question, total removal of the pollutants which disturb a biological purification stage is generally only possible by means of a combination of different and/or multi-stage methods. This requires a considerable expense for putting into operation and operating systems suitable for this purpose. Because of the partially rapidly changing composition of the water, those methods are particularly interesting which can be reliably regulated during continuous operation and are thus economical to operate.
Chloro-organic compounds can be separated from an aqueous phase by liquid-liquid extraction; however, total separation is only assured by means of a four-stage extraction. A further disadvantage is the fact that emulsions form in seepage water and an adsorption stage must be added after the extraction.
As a result of the stripping of halogen-organic pollutants with steam or air, the pollutants are distributed both into the strip phase as well as into the actual water phase so that the halogen-organic pollutants contained in them must be removed from both phases by means of further methods, e.g. adsorption or combustion.
Evaporation methods are energy-intensive and, in addition, halogen-organic pollutants, including not only short-chain halogenated hydrocarbons but even perchlorinated dibenzodioxins and dibenzofurans, can be expelled with the vapors. Therefore, other purification steps, e.g. adsorption on activated carbon, must be included.
The adsorption of aromatic, heteroaromatic, cycloaliphatic and aliphatic halogen compounds contained in highly contaminated waste water or seepage water on activated carbon can only be considered as a post-treatment stage since a direct use would require an extremely large amount of carbon and, in addition, a multi-stage adsorption system. Moreover, it would then be necessary to dispose of large amounts of contaminated activated carbon.
The determination of AOX is also based on the adsorption of halogen-organic pollutants on activated carbon: The halogen-organic pollutants are absorbed along with other water components on a very pure, halogen-free activated carbon (e.g. Merck, Darmstadt, item No. 2216); the chlorine content is determined in a known manner after incineration.
Experience with the treatment of seepage water with inclusion of adsorptive measures are disclosed in the journal "Korrespondenz Abwasser" [Waste Water Correspondence] 35, 9/1988, pp. 927-930. A multi-stage adsorption system using clays and activated carbons did not provide a reliable reduction of the AOX value below 1 mg/1. Better results can be obtained if an activated-carbon treatment by means of a stirring-in technique is followed by a fixed-bed filtration; however, this increases the expense. Frequently, additional treatment stages are necessary in the presence of readily volatile halogenated hydrocarbons such as especially C.sub.1 - and C.sub.2 haloalkanes as well as C.sub.2 haloalkenes.
It is also known that pollutants can be eliminated from waste water by means of flocculation or precipitation using, in particular, compounds of trivalent iron and the formation of iron (III) hydroxy complexes. The pollutants are partially enclosed in the floc and/or adsorptively and/or chemically bound in the form of Fe complexes, which renders them separable. Thus, for example, the COD and BOD values of seepage water can be lowered; however, combination with an absorption on activated carbon is considered necessary--cf. H. J. Ehrig in "Deponie: Ablagerung von Abfallen [Waste Dump: Storage of Refuse]/ K. J. Thome-Kozmiensky" (1987), pp. 560-579. In order to reduce the organic halogen content to values below 1 mg Cl/1 water, it is necessary to use a flocculation precipitation with iron (III) chloride, followed by a treatment with activated carbon--cf. A. Denne and E. Ecker in "Altlasten [Abandoned Polluted Areas]/K. J. Thome-Kozmiensky" (1987), pp. 649-656.
Oxidation with hydrogen peroxide in the presence of a catalytic amount of Fe.sup.2+ also has been evaluated for the treatment of seepage water with chloro-organic compounds which are difficult to degrade biologically--cf. E Gilbert and F. Bauer, Kernforschungszentrum Karlsruhe [Karlsruhe Atomic Research Center], KfK 4030, Febr. 1986. A large part of the organic pollutants can be degraded at a pH below 5 using 1 g H.sub.2 O.sub.2 per g of chemical oxygen demand (COD), an H.sub.2 O.sub.2 / Fe.sup.2+ molar ratio of 10 : 1 (Fenton's reagent) and a reaction time of about one hour. Under these conditions, it was possible to reduce the AOX value as a measure of halogen-organic pollutants, but not much below 1 mg/1. If the pH is adjusted to 7-8 after the oxidation, iron (III) hydroxy complexes (=iron (III) oxide hydrate) precipitate, which contain a part of the organic carbon, adsorbed and enclosed; however, this has only a small effect on the residual content of chloro-organic pollutants in the treated water and it was possible to reduce the AOX value only by a total of about 92% even when a biological purification stage was added.